This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C xc2xa7119 from an application entitled Apparatus And Method For Multi-Access Conference Call In Exchange System earlier filed in the Korean Industrial Property Office on Dec. 30, 1998, and there duly assigned Serial No.""s 98-60841 and 98-60843 by that Office.
1. Field of the Invention
The present invention relates to a multi-access conference call apparatus and method in an exchange system, which allow a plurality of subscribers to communicate with each other.
2. Description of the Related Art
Private exchanges are commonly used in most companies and offices. Typically, the private exchange includes a private automatic branch exchange (PABX) and a keyphone system. The private exchange, which uses a telephone line between a private branch exchange (PBX) and a telephone exchange, allows an interphone-to-telephone connection and an interphone-to-interphone connection.
Such a private exchange also provides a conference call function among a plurality of subscribers. As for the conference call function, a plurality of subscribers communicate with each other through interphone lines connected to their own terminals, wherein the number of participants, i.e., the conference group size, is predetermined by the private exchange. In other words, the conference participants can listen to the voices of all the participants, and can transmit their own voice to the other participants at any time. The conference call function, also known as a paging function for paging one or more extensions, provides advantages when a group of participants cannot gather at one point for a conference.
FIG. 1 is a block diagram of a conventional multi-access conference call apparatus in an exchange system. The conference call apparatus of FIG. 1 includes a plurality of continuously variable slope delta modulation (CVSD) coders/decoders (CODECs) 100, 102 and 104, and a plurality of operational (OP) amplifiers 106, 108 and 110. The CVSD CODECs 100, 102 and 104 decode CVSD data received from a plurality of subscriber channels, convert the decoded data to analog signals, and output the analog signals to the OP amplifiers 106, 108 and 110, respectively. The OP amplifiers 106, 108 and 110 sum and amplify the received signals, and return the amplified signals to the CVSD CODECs 100, 102 and 104, respectively. The CVSD CODECs 100, 102 and 104 encode the signals from the OP amplifiers 106, 108 and 110, respectively, and transmit the encoded data to the corresponding subscriber channels.
However, since the conventional conference call apparatus transmits analog signals to the OP amplifiers 106, 108 and 110, it is prone to noise during signal transmission. Also, when it is required to increase the group size, the scale of hardware must be extended. That is, more CVSD CODECs and OP amplifiers, corresponding to the increased group size, are required.
An object of the present invention is to provide a multi-access conference call apparatus and method in an exchange system, in which received continuously variable slope delta modulation (CVSD) data are digitally transmitted to each of a plurality of subscriber terminals.
According to an aspect of the present invention, there is provided a multi-access conference call apparatus in an exchange system, which permits a number of subscribers to communicate with each other using their own terminal, the conference call apparatus comprising: a digital signal processing unit for converting a signal of a first digital signal type from each of a plurality of subscriber channels to a signal of a second digital signal type, for summing the signals of the second digital signal type of all subscriber channels except for the signal from the subscriber""s own channel, and for converting the summed data for each subscriber channel back to the signals of the first digital signal type, to output the resulting signals of the first digital signal type to each subscriber channel; and a control signal generator for generating control signals for transmitting the signals of the first digital signal type input from each subscriber channel, to the digital signal processing unit, and transmitting the signals of the first digital signal type output from the digital signal processing unit, to each corresponding subscriber channel.
According to another aspect of the present invention, there is provided a multi-access conference calling method, which permits a number of subscribers to communicate with each other using their own terminal, in an exchange system, the conference calling method comprising the steps of: (a) a subscriber pressing a start key of a his or her terminal for a conference call with the other subscribers; (b) the exchange system converting a signal of a first digital signal type received from each subscriber channel into a signal of a second digital signal type; (c) the exchange system summing the signals of the second digital signal type of all subscriber channels except for the subscriber""s own channel, for each subscriber channel; (d) the exchange system converting the summed signals of the second digital signal type to the signals of the first digital signal type, and transmitting the resulting signals of the first digital signal type to each corresponding subscriber channel; and (e) the subscriber pressing a termination key so as to terminate the conference call.